Print hammer with high repetition rate

ABSTRACT

A print hammer having a repetition rate of at least a few hundred cycles per second is disclosed. The high repetition rate is achieved by employing an actuating arm which is electromagnetically driven but most is non-magnetic. The actuating arm is designed to have a small moment of inertia and so that the center of percussion strikes the electromagnet. The electromagnet is a low inductance device. The longitudinal motion of the printing hammer is at least twice the distance travelled by the center of percussion of the actuating arm. The moment of inertia of the printing hammer is kept low by making it of lightweight material and providing a central cavity therein. Impression control is provided by having an energy absorbing means included in the cavity of the hammer. The actuating arm is inhibited from rebounding from its home position because the backstop includes an anti-rebound material. A single spring means is provided to restore the hammer and the actuating arm to their at rest position. Circuit means are provided to open circuit the electromagnet before the hammer has reached the printing position.

Unite States atet [191 Herbert 51 Apr. 10, 1973 75 Inventor: Donald G.Herbert, Pittsford, N.Y.

[73] Assignee: The Singer Company, San Leandro,

Calif.

[22] Filed: Dec. 7, 1970 [21] Appl. No.: 95,645

[52] US. Cl. ..101/93 C [51] Int. Cl. ..B41j 9/42 [58] Field of Search..101/93 C, 287, 297, l01/109, 93 MN [56] References Cited' UNITEDSTATES PATENTS 1,780,674 11/1930 Ewald ..101/109 2,787,210 4/1957Shepard ..101/93 C 2,874,634 2/1959 Hense ..101/93 C 3,090,297 5/1963Wilkins et al. ..101/93 C 3,139,820 7/1964 Kittler ..lOl/93 C 3,152,54010/1964 Pensavechia et al.. ..101/93 C 3,266,418 8/1966 Russo ..101/93 C3,266,419 8/1966 Erpel et al. ...101/93 C 3,315,597 4/1967 Elsner101/109 3,386,376 6/1968 Mutz et al..... ...l0l/93 C 3,504,623 4/1970Staller ..101/93 C Primary ExaminerWilliam B. Penn Attorney-George W.Killian, Patrick J. Schlesinger, Charles R. Lepchinsky and Jay M. Cantor[5 7] ABSTRACT A print hammer having a repetition rate of at least a fewhundred cycles per second is disclosed. The high repetition rate isachieved by employing an actuating arm which is electromagneticallydriven but most is non-magnetic. The actuating arm is designed to have asmall moment of inertia and so that the center of percussion strikes theelectromagnet. The electromagnet is a low inductance device. Thelongitudinal motion of the printing hammer is at least twice thedistance travelled by the center of percussion of the actuating arm. Themoment of inertia of the printing hammer is kept low by making it oflightweight material and providing a central cavity therein. Impressioncontrol is provided by having an energy absorbing means included in thecavity of the hammer. The actuating arm is inhibited from reboundingfrom its home position because the backstop includes an anti-reboundmaterial. A single spring means is provided to restore the hammer andthe actuating arm to their at rest position. Circuit means are providedto open circuit the electromagnet before the hammer has reached theprinting position.

16 Claims, 3 Drawing Figures PATENTEUAPR 1 01975 Fig. 3

Fig. 2

INVENTOR. DONALD s. HEBERT AGENT PRINT HAMMER WITH HIGH PETITIONBACKGROUND OF THE INVENTION In the impact printing art, a wide varietyof printing techniques have been used, including those employed in theubiquitous typewriter, the drum printer, the wheel printer and the chainor belt printer. With drum and/or chain printers, it is conventional toprovide a print hammer for each character position and therefore, insuch applications, each print hammer operates only once per printed lineand therefore, other considerations and components usually limit thespeed of operation. That is, the recycling rate of the printing hammeris not usually a limiting factor in those applications which employ anindividual print hammer for each printing position. In other types ofprinters, notably the wheel or disc printer, it is not unusual to employa single print hammer. In such applications, the single print hammer,together with the printing wheel or disc, must movecharacter-by-character relative to the document and the hammer must gothrough an operating cycle for the printing of each character. In suchapplications, the maximum frequency within which the hammer may berecycled often limits the printing speed. More specifically, therepetition rate of the hammer determines the minimum time which mustelapse between the printing of two successive characters.

The print hammer of the present invention is intended for use in aprinter which could present successive characters, in their respectiveprinting positions, with only a few milliseconds time separation. Theprior art print hammers having the fastest known repetition raterequired at least twice as long as was desired for the application forwhich the hammer of the present invention was designed. Accordingly, thephysical characteristics and operating limits of prior art devices werestudied and new and novel methods used to obtain a new and improvedhammer having improved operating characteristics which permit ahitherto, unattained high repetition rate.

SUMMARY OF THE INVENTION The present invention is characterized bydesign considerations which provide optimum operating characteristics.These characteristics are provided through use of carefully selectedcomponent materials and the incorporation of desired characteristics bygiving due consideration to every feature of the design. For example,the location of center of gravity and the center of percussion of thehammer actuating arm have been carefully and judiciously placed atpositions which allow optimum operating characteristics. In addition,the moment of inertia of moving parts has been reduced to a minimalvalue to facilitate rapid motions and high repetition rates. Thefeatures which characterize the invention will be found in the followingspecification and the new and novel aspects of the invention aredistinctly set forth in the claims annexed to and forming a part of thisspecification. Some of the objects of the invention are:

To provide a print hammer for use in a character-bycharacter printerwhich has a higher repetition rate than prior art hammers;

To provide a print hammer which compensates for document thickness byhaving an energy absorbing structure which are returned to their at restposition by a single spring;

To provide an actuating armature which has the center of gravity and thecenter of percussion critically located to prolong the life of thearmature and its associated pivot;

To provide a structure having a minimum moment of inertia consistentwith the required range of motion of the hammer;

To provide an actuating armature backstop which substantially eliminatesany tendency for the armature to rebound from the backstop and whereinthe hammer and operating structure have a prolonged life and require aminimum of field adjustments;

These objects, together with other objects, advantages and features ofthe invention, together with a manner of implementing them will becomemore apparent as the following description is considered together withthe drawing.

BRIEF DESCRIPTION OF THE DRAWING The inventive characteristics of thehigh repetition rate print hammer will be more clearly understood whenreference is bad to the following description considered together withthe accompanying drawing, which comprises three figures and wherein:

FIG. 1 is a view of an assembly incorporating the invention;

FIG. 2 is a cross-section view of the hammer assembly of FIG. I, and

FIG. 3 is a cross-section along line 3--3 of FIG. 2.

In accordance with standard drawing practice, a given element of theembodiment incorporating the invention is always identified by the samereference numeral in all figures.

DESCRIPTION OF THE PREFERRED EMBODIMENT ture 10 are mounted on, andsupported by, a mounting plate 15, with mounting holes 16 and 17 (seeFIG. 2), upstanding portions 18 and 19 for supporting and guiding alongitudinal hammer 31, and upstanding portion 20 for supportingbackstop screw 21 and impression control screw 22. Frame members 24 and25 provide support for pivot pin 26 on which longitudinal actuatingmeans 27 is pivoted. An electromagnetic coil 28 is wound on one leg 23of a U-shaped magnetic core 29 which is adjustably fastened to themounting plate 15 by screws 30. Connections, not shown, for selectivelycompleting an electrical circuit to the coil 28 are provided.

The longitudinal hammer 31 is of a rectangular configuration with arectangular cross section. More specifically, the longitudinal hammer 31comprises two sides 32 and 33 and ends 34 and 35. Coupled to end 35 isthe hammer anvil 36 which is made of a material having the necessaryhardness and other desirable characteristics for providing good printquality as it drives the document 37 towards the print wheel 38 toeffect a character impression. The longitudinal hammer 31 has a hollowinterior. Or, in other words, the longitudinal hammer sides 32 and 33,together with ends 34 and 35 effectively comprise a box without top orbottom. A portion of the end 34 is suitably formed to coact with thelongitudinal actuating arm 27, so that when the actuating arm 27 pivotson its pivot 26 and moves in a counterclockwise direction, as seen inFIG. 2, the longitudinal hammer 31 will be driven from right to left andguided by the upstanding portions 18 and 19 of the mounting plate 15.The hammer end 34 and the actuating arm 27 are in contact at point 71but are separable. Accordingly, when the actuating arm 27 is stopped inits motion by the contact between the magnet insert 67 and the pole face70, the hammer 31 will continue. in free flight towards the printingimpact position. The end 34 of hammer 31 also has a portion 62 formedthereon towards the interior of the longitudinal hammer 31 which servesa dual function to be described more fully hereinafter.

The longitudinal hammer 31 may be thought of as having a longitudinalaxis through the center line of the hammer 31. In response to thepivotal reciprocal motion of the longitudinal actuating arm 27, thelongitudinal hammer 31 will move reciprocally along the iongitudinalaxis of the hammer 31. As already indicated, the hammer 31 is confinedwithin a guiding channel comprising the upstanding portions 18 and 19 ofthe mounting plate and a portion of the mounting plate 15, itself. Inaddition, hammer retainer 41 provides an additional guide and retainingmeans for the longitudinal hammer 31. The hammer retainer 41 bridgesupstanding portions 18 and 19 of the mounting plate 15, and it isretained in position by screw 42. The hole 43 (see FIG. 3) in hammerretainer 41 and through which screw 42 passes is an elongated hole whichthereby permits some longitudinal motion of the hammer retainer 41relative to the screw 42. The threaded portion 48 of screw 42 isthreaded into tapped hole 49 in the mounting plate 15. The screw 42 hasa shoulder 50 which prevents turning the screw 42 far enough that thehead of the screw 42 will come in contact with the hammer retainer 41.However, the flat pressure spring 44 does provide sufi'icient pressureto hold the hammer retainer 41 against the upstanding portions 18 and 19of mounting plate 15. The pressure applied by spring 44 is not so greatthat the hammer retainer 41 may not be moved longitudinally within thelimits of the dimensions of the hole 43.

The impression control screw 22 passes through a hole in upstandingportion of mounting plate 15 and has a threaded end which engages matingthreads in hammer retainer 41. Spring 45 surrounding screw 22 iscompressed between the inner surface of the upstanding portion 20 ofmounting plate 15 and the end 46 of hammer retainer 41 to therebymaintain the head of screw 22 against the upstanding portion 20 and tomaintain the hammer retainer 41 at a maximum distance from theupstanding portion 20 of the mounting plate 15. By clockwise rotation ofthe screw 22, the hammer retainer 41 may be drawn closer to theupstanding portion 20; and by counterclockwise rotation of screw 22, thehammer retainer 41 will be caused to move away from the upstandingportion 20 of mounting plate 15 by the force of spring 45. As will beseen from another portion of this specification, the position of thehammer retainer 41 will provide an impression control means.

As may be seen in FIGS. 2 and 3, the hammer retainer 41 includes adepending portion 51 which supports and retains an impression controlenergy absorber 61 which is made of an elastomeric material. That is,the energy absorber 61 is designed and positioned to absorbpredetermined and selected quantities of energy from the hammer 31. Morespecifically, when the hammer 31 is actuated by the actuating means 27,the hammer 31 moves from its position of rest which is at the right asviewed in FIGS. 2 and 3 towards the actuated position which is at theleft. In response to this motion, the projection 62 on end 34 of thelongitudinal hammer 31 will come in contact with the energy absorber 61and thereby momentarily deform the energy absorber 61. The amount ofenergy that is absorbed by the energy absorber 61 is a function ofseveral factors including at least: the velocity and mass of the hammer31, the initial distance between the energy absorber 61 and theprojection 62, the total space between the print element 38 and theprint anvil 36, and the thickness of the document 37 as well as theforce of the spring 63 and the physical properties of the absorber 61.It should be apparent that the spacing between the energy absorber 61and the projection 62 may be adjusted by moving the hammer retainer 41in response to rotation of the impression control screw 22. Obviously,the lastmentioned adjustment will influence the maximum deformation ofthe energy absorber 61 when the hammer 31 is at its maximum leftwardposition as viewed in FIGS. 2 and 3. it should also be obvious that thethickness of the document 37 will be a factor which limits the maximumleftward position of the hammer 31. As one contemplates the energy thatis required to insure satisfactory quality printing, it will be apparentthat a lesser quantum of energy is required to print on a relativelythin document 37 than on a relatively thick document 37 of a documentpack comprising a plurality of documents and associated carbon paper.Accordingly, it will be seen that the structure shown, including energyabsorber 61 and projection 62, comprises an automatic means foradjusting the energy level of the hammer 31 at the time of printingimpact so that the energy level is a function of the thickness of thedocument. To obtain satisfactory results by this means, the elastomericmaterial used for the energy absorber 61 must have a deflection curvewhich is suitable to absorb the required quantities of energy to provideoptimum print quality. A variety of shapes of the energy absorber 61combined with the selection of the elastomeric material and the spring63 may be selected to produce the desired result.

As already indicated, the hammer 31 and the actuating arm 27 are not incontact at the time of printing impact. Thus, the energy available forprinting is in the kinetic energy of the hammer 31. As is well known,the best printing quality is obtained, in an on-the-fly printer, whenthe printing energy is derived from a hammer of low mass and highvelocity. Accordingly, the hammer 31 is designed to have a minimum mass,and the electromagnet control means 12, including actuating arm 27, aredesigned to impart a high velocity to the hammer 31.

If printing is to be down on only one type of document, the impressioncontrol means, including energy absorber 61 and projection 62, could beomitted and the desired kinetic energy adjusted by control of the airgap 69, the inductance of the coil 28 and/or the mass of hammer 31 andother well known techniques.

It should be understood that the hammer 31 is in free flight at the timeprojection 62 contacts absorber 61.

After printing impact, the hammer 31' rebounds and is urged towards itshome position by spring 63. When contact between end 34 of hammer 31 andthe actuating arm 27 is reestablished, the spring 63 helps to restorethe actuating arm.

Some consideration will now be given to the electromagnetic controlmeans 12, the electric energization of which initiates the rightward toleftward propulsion and free flight of the hammer 31. As already setforth, the screws 30 through magnetic core 29 retain the electromagneticcontrol means 12 on the mounting plate 15. Optimum positioning of thisstructure 12 may be obtained inasmuch as the holes 66 through whichscrews 30 pass are elongated to permit the desirable relative motionbetween the magnetic core 29 and the mounting plate 15. The longitudinalactuating means 27 is designed to have a minimum moment of inertia inorder to permit very fast operation and recycling thereof. Accordingly,the actuating means 27 is, for the most part, constructed of alightweight material which has the desirable and necessary qualities ofstrength and rigidity. However, -such material is not a magneticmaterial and therefore, would not be affected by the electricalenergizing of coil 28. Accordingly, the longitudinal actuating means 27has a magnetic insert 67. It should be observed that the magnetic insert67 is made of a high quality material and has the minimum dimensionswhich provide acceptable magnetic operation. In addition, the magneticinsert 67 on the actuating arm 27 has its mass located relatively closeto the pivot point 26 so that the effect of the mass of the magneticinsert 67 on the total moment of inertia of the actuating arm 27 is keptat a minimum. It should also be understood that the dimensions and massdistribution of the actuating arm 27 have been carefully selected anddesigned so that the center of percussion thereof is located atapproximately point 68. In accordance with well-known principles,relative to moving and rotating bodies, this structure imparts a purerotational movement to the arm 27 with respect to the pivot point 26.Accordingly, the wear at the pivot point 26 is minimal. In addition, astructure built in accordance with the principles set forth will bequieter in operation than structures having a center of percussion atsome other location.

In order to increase the actuating speed of the print hammer 31, thecoil 28 is designed with a minimum inductance. Also, to increase themagnetic efficiency of the circuit, the air gap 69 between the magneticinsert 67 and the pole faces 70 of the magnetic core 29 is held to aminimum. However, the hammer 31 must be moved through a greaterlongitudinal distance than that of the air gap 69, and it is desired toimpart a maximum velocity to the hammer 31. Accordingly, the contactpoint 71 between the actuating arm 27 and the hammer 31 is removed fromthe pivot point 26 a distance which is at least twice the distance ofthe center of percussion 68 from the pivot point 26. Accordingly, thelongitudinal motion of contact point 71 and hammer 31 will be at leasttwice the distance of the air gap 69. The hammer 31 will also move anadditional amount in free flight. In the design of the actuating arm 27,careful consideration must be given to the effect of the moment ofinertia of the arm 27 as the contact point 71 is moved further away fromthe pivot point 26. An optimum balance between high velocity at point 71and the detrimental affect of an increased moment of inertia must beobtained.

In accordance with standard procedures and good design practice whichare well known to those skilled in the art of high speedelectromechanical mechanisms, any of a variety of electronic techniques(not shown) may be employed for energizing coil 28 to initiate actuationof arm 27 and to de-energize the coil 28 at an optimum time which willassure that the hammer 31 will be propelled to its maximum leftwardposition at maximum velocity and yet be ready to return towards the restposition when the hammer 31 rebounds from the printing impact and isdriven towards the rest position by spring 63. That is, the hammerstructure 10 is designed for an on-the-fly printer wherein the printwheel 38 is constantly rotating. Accordingly, the anvil 36 must strikethe document 37 and press it against a character on the type wheel 38and start on its return motion in a minimum period of time in order toavoid smearing the print on the document. Therefore, by the time thecharacter from the print wheel 38 has been printed on the document 37,the coil 28 has been deenergized and the hammer 31 is free to move toits rightward position and the actuating arm 27 is free to pivot in theclockwise direction about pivot pin 26. As previously mentioned, theenergy absorbing element 61 coacting with the projection 62 controls theresidual energy of the hammer 31 at the time of printing impact. Itshould be observed that the energy absorber 61 is mounted on the hammerretainer 41 and that the energy absorber 61 does not move with thehammer 31 except to the extent that the energy absorber 61 ismomentarily deformed by the projection 62 on the hammer 31. Coupledbetween the energy absorber 61 and the projection 62 is a compressionspring 63. The energy stored in the compression spring 63 when thehammer 31 is propelled to its leftward position is used to drive thehammer 31 and the actuating arm 27 to their rightward and clockwisepositions, respectfully.

The clockwsie rotational limit of the actuating arm 27 is controlled bybackstop screw 21 which has an elastomeric insert 76 with which theactuating arm 27 comes in contact. The elastomeric insert 76 serves tocompletely damp the motion of the actuating arm 27 so that it does notrebound from the elastomeric insert 76. Accordingly, the actuating arm27 is immediately available for a reactuation. The air gap 69, andtherefore, the total maximum travel of the hammer 31 may be controlledby the rotation of backstop screw 21. That is, to reduce the air gap 69,the backstop screw 21 may be turned in a clockwise direction; and toincrease the air gap 69, the backstop screw 21 may be rotatedcounterclockwise. In addition, of course, a course control over the airgap space 69 may be obtained by loosening screws 30 and positioning themagnetic core 29 relative to the frame 15.

The backstop screw 21 is not located in line with the center ofpercussion 68 as it is desired to have spring 63 apply a slight force toposition actuating arm 27 in a fixed location. That is, if the backstopscrew 21 were in line with the center of percussion 68, the actuatingarm 27 would be floating and the air gap 69 would not be constant andtherefore, the operating characteristics would not be consistent. Alsowith the backstop screw 21 closer to the point 71, it is easier toprovide the desired adjustment of the air gap 69.

In order to hold and retain the document 37 in the desired positionbetween the print wheel 38 and the hammer anvil 36 during printing,appropriate and conventional paper guides are provided. For example,paper guide 80 is attached to upstanding portion 18 of mounting plate 15by screws 81. By means not shown and which do not form a part of thepresent invention, the paper guide 80 is spring biased towards the printwheel 38 to lightly clamp the document 36 between the paper guide 80 andanother document supporting paper guide (not shown) between the printwheel 38 and the document 37. Obviously, the paper guide 80 has awindow, or cutaway portion, so that printing may be facilitated. Thedrawing of the present invention does not illustrate the use of any typeof inking ribbon between the print wheel 38 and the document 37. This isbecause in the embodiment illustrated, the print wheel 38 is inked as itpasses over an inked roller. However, if desired, a conventional inkedribbon could be employed.

While there has been shown and described what is considered at presentto be the preferred embodiment of the invention, modifications theretowill readily occur to those skilled in the related arts. It is notdesired, therefore, that the invention be limited to the specificembodiment shown and described, and it is intended to cover in theappended claims, all such modifications as may fall within the truespirit and scope of the invention.

What is claimed is:

l. A print hammer for an on-the-fly printer comprising:

a. a longitudinal hammer having a central longitudinal cavity andsupported for linear reciprocal motion along the longitudinal axisthereof from a normal first position toward a second print position;

b. a hardened hammer face secured to one end of said longitudinal hammerfor providing printing impact;

c. electromagnetic drive means for contacting said hammer at the endopposite the hammer face for imparting a fixed quantum of energy theretoas said drive means drives said hammer from said first position towardsaid second print position;

d. adjustable energy absorbing means positioned within said cavity andcooperating with said longitudinal hammer for absorbing a predeterminedportion of said fixed quantum of energy wherein said predeterminedportion is a function of the magnitude of the linear motion of saidlongitudinal hammer from said first position toward said secondposition,

e. frame means for supporting and guiding said longitudinal hammer; andwherein said f. energy absorbing means comprises:

1. a first element adjustably secured to the frame and extending intosaid hammer cavity; and

2. a second element formed on the interior of said hammer and extendinginto said cavity along the longitudinal axis of the hammer to contactsaid first element when the hammer is driven toward its print position.

2. The combination as set forth in claim 1 and including spring meanspositioned within said cavity and cooperating with said first and secondelements for biasing said longitudinal hammer toward said firstpositron.

3. The combination as set forth in claim 1 wherein said adjusting meansincludes screw means securing the second element to the frame means foradjusting the position of said second element relative to said frame andalong the longitudinal axis of the hammer so that said predeterminedportion of said fixed quantum of energy which is absorbed may beselectively adjusted.

4. The combination as set forth in claim 1 wherein said drive meanscomprises:

a. a longitudinal actuating arm pivotally supported at one end forlimited reciprocal motion and having the other end thereof positioned tocontact said longitudinal hammer to drive the hammer toward its secondposition and wherein the longitudinal axes of said hammer, saidactuating arm, and the pivot of said arms are substantially mutuallyperpendicular.

. The combination as set forth in claim 4 and includelectromagneticcontrol means to selectively apply a driving force to said actuating armto impart said fixed quantum of energy to said longitudinal hammer whenthe arm contacts the hammer to drive it toward its second position.

6. The combination as set forth in claim 5 wherein said electromagnetcontrol means includes pivot limiting means for limiting the pivotalmotion of said longitudinal actuating arm when said longitudinalactuating arm is moving in the direction to drive said longitudinalhammer toward said second position, and wherein said driving force isterminated before said longitudinal hammer is completely driven to saidsecond position.

7. The combination as set forth in claim 6 and wherein the center ofpercussion of said longitudinal actuating arm is situated in the area ofthe arm which engages said limiting means.

8. The combination as set forth in claim 7 and wherein the distancealong said pivot to said center of percussion is less than the distancefrom said center of percussion to the point of contact between saidother end of said actuating arm and said longitudinal hammer.

9. The combination as set forth in claim 8 and including a single springmeans for urging said longitudinal hammer and said longitudinalactuating arm toward said first position.

10. The combination as set forth in claim 9 and including a backstop forlimiting the pivotal motion of said longitudinal actuating arm as saidlongitudinal hammer is urged toward said first position thereof by saidsingle spring means.

11. The combination as set forth in claim 10 wherein said backstopincludes a vibration damping material.

12. The combination as set forth in claim 5 wherein said longitudinalactuating arm comprises a nonmagnetic material which is lightweight incomparison with magnetic material and a magnetic material insert isprovided in the arm adjacent to said electromagnetic control means forcontrol of the reciprocal motion of said arm thereby.

13. The combination as set forth in claim 12 wherein said longitudinalhammer comprises a nonmagnetic material which is lightweight incomparison with said magnetic material.

14. The combination as set forth in claim 13 wherein the moment ofinertia of said longitudinal actuating arm is less than the moment ofinertia of said longitudinal hammer.

15. The combination as set forth in claim 14 wherein the distance fromthe center of gravity of said longitudinal actuating arm to the axis ofsaid longitudinal hammer is at least twice the distance from the centerof gravity of said longitudinal actuating arm to the pivot pointthereof.

16. The combination as set forth in claim 15 and including a. singlespring means for urging said longitudinal hammer toward said firstposition thereof and the arm to one limit of its range of reciprocalmovement.

* l t IF

1. A print hammer for an on-the-fly printer comprising: a. alongitudinal hammer having a central longitudinal cavity and supportedfor linear reciprocal motion along the longitudinal axis thereof from anormal first position toward a second print position; b. a hardenedhammer face secured to one end of said longitudinal hammer for providingprinting impact; c. electromagnetic drive means for contacting saidhammer at the end opposite the hammer face for imparting a fixed quantumof energy thereto as said drive means drives said hammer from said firstposition toward said second print position; d. adjustable energyabsorbing means positioned within said cavity and cooperating with saidlongitudinal hammer for absorbing a predetermined portion of said fixedquantum of energy wherein said predetermined portion is a function ofthe magnitude of the linear motion of said longitudinal hammer from saidfirst position toward said second position, e. frame means forsupporting and guiding said longitudinal hammer; and wherein said f.energy absorbing means comprises:
 1. a first element adjustably securedto the frame and extending into said hammer cavity; and
 2. a secondelement formed on the interior of said hammer and extending into saidcavity along the longitudinal axis of the hammer to contact said firstelement when the hammer is driven toward its print position.
 2. a secondelement formed on the interior of said hammer and extending into saidcavity along the longitudinal axis of the hammer to contact said firstelement when the hammer is driven toward its print position.
 2. Thecombination as set forth in claim 1 and including spring meanspositioned within said cavity and cooperating with said first and secondelements for biasing said longitudinal hammer toward said firstposition.
 3. The combination as set forth in claim 1 wherein saidadjusting means includes screw means securing the second element to theframe means for adjusting the position of said second element relativeto said frame and along the longitudinal axis of the hammer so that saidpredetermined portion of said fixed quantum of energy which is absorbedmay be selectively adjusted.
 4. The combination as set forth in claim 1wherein said drive means comprises: a. a longitudinal actuating armpivotally supported at one end for limited reciprocal motion and havingthe other end thereof positioned to contact said longitudinal hammer todrive the hammer toward its second position and wherein the longitudinalaxes of said hammer, said actuating arm, and the pivot of said arms aresubstantially mutually perpendicular.
 5. The combination as set forth inclaim 4 and including: a. electromagnetic control means to selectivelyapply a driving force to said actuating arm to impart said fixed quantumof energy to said longitudinal hammer when the arm contacts the hammerto drive it toward its second position.
 6. The combination as set forthin claim 5 wherein said electromagnet control means includes pivotlimiting means for limiting the pivotal motion of said longitudinalactuating arm when said longitudinal actuating arm is moving in thedirection to drive said longitudinal hammer toward said second position,and wherein said driving force is terminated before said longitudinalhammer is completely driven to said second position.
 7. The combinationas set forth in claim 6 and wherein the center of percussion of saidlongitudinal actuating arm is situated in the area of the arm whichengages said limiting means.
 8. The combination as set forth in claim 7and wherein the distance along said pivot to said center of percussionis less than the distance from said center of percussion to the point ofcontact between said other end of said actuating arm and saidlongitudinal hammer.
 9. The combination as set forth in claim 8 andincluding a single spring means for urging said longitudinal hammer andsaid longitudinal actuating arm toward said first position.
 10. Thecombination as set forth in claim 9 and including a backstop forlimiting the pivotal motion of said longitudinal actuating arm as saidlongitudinal hammer is urged toward said first position thereof by saidsingle spring means.
 11. The combination as set forth in claim 10wherein said backstop includes a vibration damping material.
 12. ThecomBination as set forth in claim 5 wherein said longitudinal actuatingarm comprises a nonmagnetic material which is lightweight in comparisonwith magnetic material and a magnetic material insert is provided in thearm adjacent to said electromagnetic control means for control of thereciprocal motion of said arm thereby.
 13. The combination as set forthin claim 12 wherein said longitudinal hammer comprises a nonmagneticmaterial which is lightweight in comparison with said magnetic material.14. The combination as set forth in claim 13 wherein the moment ofinertia of said longitudinal actuating arm is less than the moment ofinertia of said longitudinal hammer.
 15. The combination as set forth inclaim 14 wherein the distance from the center of gravity of saidlongitudinal actuating arm to the axis of said longitudinal hammer is atleast twice the distance from the center of gravity of said longitudinalactuating arm to the pivot point thereof.
 16. The combination as setforth in claim 15 and including a single spring means for urging saidlongitudinal hammer toward said first position thereof and the arm toone limit of its range of reciprocal movement.